Fire-rated panels are used as building structures in a variety of applications, including roof panels, wall panels and fire doors. While the fire-rated panel will vary somewhat for the particular application involved, e.g. a roof panel or wall panel or fire door, all of these fire-rated panels have in common the ability to prevent burn-through of fire, under standard test conditions, for a minimum length of time.
There are two primary types of fire-rated panels, i.e. a non-combustible panel and a combustible panel. The non-combustible panel is made of inorganic materials, e.g. steel, fiberglass, mineral and gypsum board, and the like. Typically, a non-combustible panel comprises two sheet steel faces which sandwich therebetween some insulating material, such as fiberglass. Since none of the materials of the panel are combustible, i.e. the materials are all inorganic materials, these panels are referred to the art as non-combustible panels. The other type of fire-rated panel is referred to in the art as a combustible panel and is made of, at least in part, combustible materials, e.g. wood or wood products.
Non-combustible panels have decided disadvantages. Firstly, such panels, with or without fiberglass insulation between the sheet steel faces, are very heavy and are very difficult to render in an aesthetically pleasing manner. While such panels may be painted, or likewise decorated, such steel panels very of ten do not fit into decorative schemes for buildings. Accordingly, non-combustible fire-rated panels are generally limited to uses in industrial structures.
The fire-rated combustible panels, typically, will have outer faces of wood, wood veneer or plastic sheets simulating wood grain, or the like, and can be made to have a quite satisfactory aesthetic appearance and fit within decorating schemes. However, since the combustible panels will combust, the fire rating provided to these panels is, primarily, a result of a fire resistant core disposed between the outer faces of the combustible fire-rated panel.
As can be appreciated, since the fire-resistant core is the essential element for achieving a fire rating in combustible fire-rated panels, the art has expended considerable effort in providing fire-resistant core materials for the combustible fire-rated panels, and this effort has been particularly acute in connection with combustible fire-rated panels used as fire doors. Fire doors present additional problems, beyond those problems inherent in the use of the fire-rated panels for other applications, e.g. wall panels and roof panels.
In this latter regard, whether the panel is used as a roof panel, a wall panel or a fire door, the panel will require some attachment to some supporting structure. For example, wall panels require attachment to conventional wall studs and roof panels require attachment to supporting roof structures. When the panels are used as fire doors, those doors not only require attachment to the supporting structure, e.g. the door frame, but the doors must also have attached thereto associated hardware, such as lock sets, hinges, panic bars and the like. Since the fire-resistant core is normally made of an inorganic, non-combustible material, for example, gypsum board, considerable difficulty has been experienced in the art in mounting the necessary hardware to the door. This is because the non-combustible cores of such doors, generally, have very poor fastener-holding properties, e.g. sufficient properties for holding screws, nails, bolts and the like. As a result, with combustible fire-rated doors, special efforts have been required to provide increased fastener-holding properties, which is not normally common to other uses of the fire-rated panel, e.g. the wall and roof panels.
In view of the foregoing, while the invention is fully applicable to use with combustible fire-rated panels in general, in view of the special problems of fire doors, and to be more concise, the invention will be described hereinafter in connection with the embodiment of a combustible fire-rated door.
Typically in past prior art, the fire-resistant core was made with asbestos. Various compositions of asbestos were proposed in the past prior art, but with the advent of health concerns in connection with asbestos, the art sought substitutes for the past asbestos-containing fire-resistant cores. U.S. Pat. No. 4,075,804, issued to Zimmerman, proposed a combustible fire-rated door, or other like panel, as described above, which is free of asbestos. That patent proposed providing a fire-resistant core material where a slurry of ingredients is poured into a horizontal mold and cured in an autoclave, similar to the manner in which the past asbestos-containing fire resistance cores were made. However, instead of using asbestos fibers in that slurry, that patent suggests substituting for the asbestos fibers a combination of vermiculite, sisal fibers and fiberglass. Calcium silicate, which is a binder for the ingredients, is also used in that composition, in the same manner in which it was used in connection with the past asbestos-containing fire-resistant cores. However, although this core does not contain asbestos, it does suffer from the same disadvantages as the past fire-resistant cores made with asbestos in that it has very poor fastener-holding properties, and special provisions, as explained more fully below, are required for use of that core in producing fire-rated doors.
U.S. Pat. No. 5,045,385, issued to Luckanuck, proposed an improvement, wherein the slurry from which the cores were cast included wood chips and a curable phenolic resin. This provides greater rigidity to the core, so as to avoid inadvertent breaking or cracking of the cast cores during handling and manufacture of doors, and the wood chips considerably improved the fastener-holding properties, referred in the art as "screw holding power". However, the screw holding power of that core is still unacceptable for door use, and special provisions are required for mounting hardware to such a fire-rated door.
U.S. Pat. No. 5,171,366, issued to Richards et al, proposes a similar core to that proposed by Luckanuck, but instead of wood chips, proposes a combination of calcium sulfate and pulp paper fibers. The screw holding power of that core is increased, but, again, the screw holding power is not sufficient that fire doors can be made without special provisions.
In this latter regard, the special provisions typically used for making combustible fire-rated doors with conventional fire-resistant cores includes cutting the core where hardware is to be mounted, e.g. hinges, lock sets, panic bars and the like, and replacing those cut portions with dense materials which have much greater screw holding power. A number of such dense materials have been proposed by the art and are presently routinely used in producing combustible fire-rated doors. This, however, requires considerable labor in cutting the core and replacing those cut portions with the dense materials. Further, hardware can be mounted only where those dense materials have replaced the core. Thus, a door must be specially manufactured for specific hardware, and this considerably reduces interchangeability of such fire-rated doors and causes difficulties in the production thereof. Also, replacing the fire-resistant core with these dense materials creates a discontinuity where the dense materials replace the core and can cause difficulties in preventing burn-through of the fire.
Accordingly, it would be of a substantial advantage to the art to provide a fire-resistant core for combustible fire-rated panels, especially fire doors, which has screw holding power throughout the entire core which is more than sufficient to retain hardware or other fastening devices at any place on the panel. It would be a further advantage to the art to provide such a core which provides increased rigidity of the panel, and especially a fire-rated door, and which core can be inexpensively made and can be accommodated in automatic processes for producing the fire-rated panels, especially fire-rated door, and which do not require any special labor or dense inserts.